Going to experiment with lidless vs. holey lid. Reading through the site, some put holes on top, some on sides, some cut off the whole rear of the airbox lid, some enlarge the stock hole locations, etc etc. General consensus seems to be that a holey lid is the way to go with two or four holes. Where are yours, and if you did it again, would you change the placement of them (other than duct taping over them)? Also, how large are the holes, and what differences did you make (or notice)?
TIA
Jeff

Like you I have read post upon post about air box mods and I think you have covered the main mods people tend to be doing.

Once I have my powervalves sorted I am going to drill 2 x 30mm holes after giving the bike a run if it is still rich. That way I can assess and drill mor holes if necessary. I have hrc shortened chambers with custom cans and the PGM wire splice.

The problem with the stock airbox is that it does not flow as much air as the carbs are able to, and therefor limits the power thw engine could be producing.

The answer is to remove this restriction of course, and the ultimate is no airbox, or the HRC setup. Fine for the track, but a bit extreme for the road.

Next best is no airbox lid, but I for one find this extremely loud.

The last option is to open the lid up to allow as much air in as the carbs can flow, but how you do it is up to you. Trial and error seems to have discovered that four 1 inch wide holes give sufficient air. I decided to simply cut off the restictive trumpets, and keep the intake in the same genral area as Honda made it, but the overall effect is the same.

I have also removed the web from the airbox lid, though I've no idea if this has any effect or not. I always intended to remove the one from beneath the filter, but somehow never got round to it...
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

How is the noise with the snorkel area cut out, compared to no lid at all?
Thanks
Gurgling Jeff, the hungry American.....

After much dyno time on StephenRC45's MC18 and some MC21's, 4x 20mm holes in the front slope of the airbox lid was been deemed the best solution for most road bikes.

It works better than any other modification, but he would still tape off two holes to richen it up a tad on a cold night leaving my place.

NO delimited NSR should make below 60hp (except an MC16) with the airbox modded like this. If it does, then it's on the way out.

Leaving the lid off tends to make them seem rather weak (limp, not lean!) -- you're better off with open carbs or a modified lid. Whatever you do it needs careful setting up, as once you start fiddling they become very sensitive to any changes.

Best part of 75hp on 98 pump unleaded out of his MC21 (without ram air) says who are we to argue with his results.
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Andy.
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Awesome. Thank you very much, Andy. I'm sure that will be very useful to a lot of us.
Jeff, OH

jeff, OH wrote:How is the noise with the snorkel area cut out, compared to no lid at all?

Far quieter, but with a lovely growl.
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Put four 20mm holes in the lid, as Andy suggested. Bike won't rev-out, like it wouldn't do before I completely removed the lid. Ordering some smaller MJs. Currently have 148 front, 145 rear. Will keep you posted. DO like the sound better.
Thanks
Jeff, OH

No specific jetting chat in the public area please.
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Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

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Dave Ett wrote:The problem with the stock airbox is that it does not flow as much air as the carbs are able to, and therefor limits the power thw engine could be producing....

Dave, does this apply to the MC16 as well or is it ok with the smaller carbs ?

The MC16 was never restricted. It makes as much power as Honda intended it to at the time, but it can make more if you're prepared to monkey about with the carbs and transfer ports.
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

The transfer ports on the MC16 arn't that bad. However they suffer with very small exhaust ports (cured by using MC18/21 barrels and heads) and poor crank cases (cured by alot of work).
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If I have to take the carbs off once more...

Dave Ett wrote:
I have also removed the web from the airbox lid, though I've no idea if this has any effect or not. I always intended to remove the one from beneath the filter, but somehow never got round to it...

Currently doing some reading about how to best handle the intake restriction...

I think it is not a good idea to remove the web in the the airbox which separates the "two" air boxes. There must be a reason Honda has spent the effort to design and manufacture this separarting wall. Some might argue it's just there to support the centre of the filter but I think there is a different reason.

Because of the 90° twin, the intake phases of the two cylinders overlap to a certain degree. The second piston is just moving at its highest speed (i.e. biggest vaccum) when the first is approching TDC i.e. if the airbox, filter and airbox intake holes restrict the free flow of air to piston 2, the flow caused by piston 1 will be "starved" by piston 2 sucking stronger.

I think the fact that Honda even gave the air box separate intake pipes strongly supports this theory.

Just some thoughts, maybe too theoretical...

Tere are reed valves, so one cylinder can't suck mixture from the other.

With a large aperture for air to rush in to theairbox, I'm not sure I believe that one cylinder can starve the other of air. Maybe in the original restricted setup, but once you've opened up the intake both could be on the intake stroke and they'd still get enough air.

I didn't mean to say that one piston can suck gas from the other crankcase. This is of course prevented by the reed valves. I was trying to express that the piston moving at its max speed starves the other piston almost at TDC. It sort of "steals" air from the area in front of the the other carb insulator.

But now that I have done more "research" on airbox design I tend to agree that the reason for the webbing is not the above. It probably has more to do with resonance in the airbox and waves travelling between the intake tubes and the carb insulator mouths. And for this, you need two airboxes.